Nitric oxide (NO) is an endogenously produced molecule that has multiple roles in physiological processes, including angiogenesis, wound healing, neurotransmission, smooth muscle relaxation, and inflammation. Nitric oxide's action on physiology is highly dependent on location, source, and concentration. It is produced in vivo by NO synthase (NOS). Low nanomolar NO concentrations are produced by eNOS and nNOS to promote vasodilation and neurotransmission, respectively. The iNOS form is capable of producing micromolar levels of NO, often responding to infection and inflammation. In the presence of superoxide (O2.−), NO will react to form peroxynitrite (ONOO—), an even greater oxidant involved in the inflammatory response. Peroxynitrite causes apoptotic or necrotic cell death through nitration of tyrosine residues in proteins, lipid peroxidation, oxidation of critical thiols, DNA strand breaks, NAD depletion and thus energy failure. NO is also a wound healing promoting agent and due to its antibacterial activity it is a promising agent for reducing implant-associated infections and promoting tissue regeneration in orthopedic procedures.
However, nitric oxide has a short half-life (<1 s) in the presence of oxygen and hemoglobin) in vivo, arising from its high reactivity with transition metals and heme-containing proteins. Due to the reactive nature of gaseous NO, its short half-life, instability during storage, and potential toxicity, including its influence on the systemic blood pressure, chemical strategies for NO storage and release have been developed in an effort to use NO's pharmacological potential. Several ways of NO release to tissues have been developed. Diazeniumdiolates (1-amino-substituted diazen-1-ium-1,2-diolate, i.e. NONOates) and S-nitrosothiols represent the two most diverse NO donor classes. Other classes are organic nitrates and metal nitrosyl compounds such as sodium nitroprusside and potassium nitrosylpentachlororuthenate.
The release of NO from several nanocarriers have been developed to avoid systemic NO side effects while transporting the NO source to the selected tissue. The selective delivery of NO to tissues in adequate concentrations is a developing area of research. These include polymeric nanoparticles, micelles, dendrimers, nanogels, gels, gold nanoparticles, silica nanoparticles and liposomes. The possibility of releasing NO before reaching the tissue site is still a major problem in particle-based systems. In addition, the rate of release of NO at the tissue site using those systems is difficult to be controlled and those where controlled release of NO is observed are mostly metal-based nanoparticle systems containing transition metals with the potential toxicity of those remaining to be tested.
One way of selectively release NO at the needed tissue is to use tissue-penetrating light (wavelengths in the near infrared region, NIR) to activate NO release from molecules. A recent technique, using a 2 photon laser irradiation where NIR photons are added to produce more energetic photons, and NIR-to-visible up-conversion, which are able to release NO from NO-containing molecules and has been developed and used in NO-containing nanoparticles. This technique permits the use of longer, tissue-penetrating wavelengths for the photochemical release of NO at the selected tissue site. The use of liposomes for photodelivering NO from NO-containing chromium complexes has also been reported, where NO is detected outside the liposome. However, a non-tissue-penetrating light wavelength was used. The technical problem to overcome is that those photocontrollable NO donors, where all of them contain transition metals, may exhibit systemic toxicity due to release of transition metal ions. In addition, those systems do not generate peroxynitrite, a species which should enhance the toxic activity of NO.
Cupferron, a carbon-bound diazenium diolate, is able to produce nitric oxide photochemically and upon enzymatic oxidation. A natural product with carbon-bound diazenium diolate structure, without the potential carcinogenicity of cupferron, is alanosine, (FIG. 1). Furthermore, the possibility of generating carcinogenic nitrosamines, as could occur after photolysis of nitrogen-bound diazeniumdiolate ions, has not been reported for carbon-bound diazeniumdiolates. Since other NO-containing compounds release NO by photosensitization, this invention proposes the photosensitized generation of NO from this type of compound. This invention proposes the photosensitized release of NO from alanosine using NIR radiation. Evidence supports the generation of peroxynitrite from air-saturated dye-alanosine solutions and from air-saturated 2-methyl-2-nitrosopropane (MNP) solutions containing a sacrificial electron donor. Although the photosensitized generation of NO from MNP has been reported previously, evidence indicating the photosensitized production of peroxynitrite by MNP in the presence of the sacrificial electron donor, hypoxanthine (HX), is described here. The present invention also used MNP to contrast the behavior of alanosine. The photosensitized production of NO could be used in photodynamic therapies of malignancies, where NO or peroxynitrite are used as toxic agents, and where nanoparticle carriers containing both the NO source and the photosensitizer, are transported to the desired tissue.
Throughout the figures, the same reference numbers and characters, unless otherwise stated, are used to denote like elements, components, portions or features of the illustrated embodiments. The subject invention will be described in detail in conjunction with the accompanying figures, in view of the illustrative embodiments.